PH and koi keeping

The PH reading of my pond always varies between 6.8-6.9.
I always have the impression that it is best to keep the ph between 7.2-7.3.
Do I need to raise the ph? And if I need to do so, how should I go about doing it?

For both the koi and the bacteria in the filters....keep the pH in the base/alkaline range (above pH of 7). A pH of 7.2 to 7.5 is a very good target range....provided it is stable. Stability may be more important that the actual value.

You may need to add alkalinity to the pond system if your supply water is very low in alkalinity, you are not changing out lots of water every week, and you have a high stockling level (more fish...more acids). You can add alkalinity by add crushed oyster shells or pieces of limestone/marble to showers, TTs, or filter chambers (typically in nylon bags). For very short term corrections you can use baking soda. But be careful with it as it goes into solution instantly....and a big quick change in alkalinity, and therefore pH, can stress the fish.

In many ways I miss the supply water we had in Dallas. It was full of limestone. Not good for house plumbing....but kept the alkalinity and pH very stable.

I do not disagree with MCA, but come at this from a different perspective. A stable pH in that range should be fine for the koi. Many mudponds in Japan have a similar pH range. The concern is the effective metabolism of the nitrifying bacteria and the risk of a pH crash if the KH is low. The use of oyster shell as suggested by MCA could be beneficial.

Water varies considerably, so your pH in itself does not cause me any concern if there are no significant swings during the course of the day and never any detectable ammonia or nitrite. It is possible to have such a pH with good KH levels, although usually KH is going to be low when the pH is below 7.0. But, water does differ. If you are using a continuous flow of fresh source water with that pH, it also impacts whether you have an issue that needs addressing. I get concerned about adjusting pH because pH is a consequence of the interaction of many components of the source water. It can be very difficult to alter pH without the koi having to endure large pH swings, and one has to consider the effect on water change practices, etc. of having to do many small water changes each week, or use constant flow, or pre-adjust pH in a separate holding facility before introducing water to the pond in large volumes. Stability is more important than a perfect pH. As koikeepers advance in their knowledge and skill at waterkeeping, altering the water to a desired softness, pH, etc. can become a goal. I think it best for most to focus on the goal of maintaining the pond parameters to match their source water, assuming the source water is suitable for koi. Aiming for 'perfect water' is better done after one has gained an understanding of their source water and is able to make the commitment of time and energy required to maintain the stability of an altered water chemistry. ...I gave up on keeping Discus years ago because the time and energy required for a few aquaria was more than the enjoyment I derived from the fish.

Thanks MCA and Mike for your kind comments.
Can I put the raw oyster shell directly into the filtation, of course I might need to clean them first I guess, or do I need to pre-treat the shells by open fire or other similar methods?
Milke, the source water has a ph reading of 6.9 to 7. The ph reading of my pond is pretty stable. The KH of the source water is in between 100-130. I have found that due to the frequent heavy rain in the past few days, the KH drops to 100-110, but in a dry season, it will go up to 120-130. You have convinced me to remain where I am and not trying to raise the ph just for now.
Maybe later. Haha!

That's right. Many mudponds in Japan ARE in the 6.8 range. But they are mud ponds. And their pH can also swing wildy throughout the day- but they are mud ponds. There is a great difference between a mud pond and a back yard garden pond. While 6.8 is survival range and even a good range because it reflects soft water, it is also a dangerous range for a closed system- especially a heavily stocked, heavily fed system. YOu had better do regular water changes religiously during warm weather on such a system to avoid a pH crash. And I'd definitely use oyster shells as a media in one of the TT systems. JR

You want shells that are clean....free of organic material. You don't to introduce strange bacteria/virus/fungus on the shells. You would not want decaying oyster or barnicle tissue in the pond system. Once free of all organic material, the shells should be OK to put in the water column (in showers, TTs, in bags in filter chambers).

Good foot note MCA! Tonight I will post a picture of the power of erosion, both mechanical and biological, on the surface of oyster shells. I like the tower idea for this reason- good erosion, good bacterial growth, unlimited oxygen supply and all attacting the hard surface of the shell 24 X7. JR

MCA and JR are giving great info. I do not know the form in which oyster shell (or other shells) are available in China. In the U.S., it can be found in crushed form at agricultural supply stores to be used as chicken grit. Some say the crushed shell should be washed to get rid of the powder and very small particles and added over time because so much surface area is exposed to the water immediately. Some say it does not really matter in practice. It seems to be widely agreed that whole shells can be added to a shower or trickle tower or chambered filter in great quantity without concern of causing any sudden change in water conditions. Restaurants are a source some use, but care needs to be exercised that the shells are clean. I think whole shells (or large pieces) are less likely to have contaminants mixed in. I think I know what JR has in mind for his photo post... should be good.

Here in the pacific northwest, Oyster shell is available for turkey grit and comes in three sizes. Nothing is added that would be harmful as chickens and Turkeys are being raised for human consumption. I'd suggest you get the biggest/largest sized grit you can get. As JR suggests a good place to
place it is in a good movement of water. I have used my wife's panty-hose that developed unsighly runs to put the oyster shell in.....

Just out of curiosity, between large sized oyster shell grits and whole oyster shells, are there any any advantages of using one over the other? The only thing I can think of is that the large sized oyster grits have more surface areas since they are smaller. Also, they are cleaner than the whole oyster shells. I am building a bakki shower out of plastic crates and was thinking of filling one of the trays up w/ oyster shells.